Integrated micro actuator and LVDT for high precision position measurements

ABSTRACT

A single housing with a non-ferromagnetic piezo-driven flexure has primary and secondary coil forms of different diameters, one coaxially inside the other, integrated in the flexure. The cylinders defining the planes of the primary and secondaries do not spatially overlap. The secondary coil forms may be wound in opposite directions and wired to provide a transformer device. Movement of the primary relative to the secondaries in the direction of the central axis of the coils can be differentially detected with high precision.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a divisional application of application Ser. No.13/959,943, filed Aug. 6, 2013; now U.S. Pat. No. 9,518,814; which is acontinuation of U.S. Ser. No. 12/587,947 filed Oct. 14, 2009, now U.S.Pat. No. 8,502,525 issued Aug. 6, 2013, which claims the benefit of U.S.Provisional Ser. No. 61/195,983 filed Oct. 14, 2008, the disclosures ofall of which applications are herewith incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to (i) linear variabledifferential transformers (LVDTs), devices that convert very smallmechanical displacements, as small as those in the sub-nanometer level,into differential voltages (and vice versa), and (ii) integrating LVDTsinto the structure of a scanning probe device such as the atomic forcemicroscope (AFM) so that certain movements of the device may beconveniently sensed and corrected if desired.

FIG. 1 shows an LVDT according to U.S. Pat. No. 7,038,443, LinearVariable Differential Transformers for High Precision PositionMeasurements, by some of the same inventors as here. This LVDT reflectsthe basic idea of these devices in the prior art that the mutualinductances between a moving primary and two secondaries change as afunction of the position of a moving part. In commercial LVDTs availablethe LVDT of U.S. Pat. No. 7,038,443, the moving part was a ferromagneticcore and the positions of the primary and the secondaries was fixed.However, because of the use of non-ferromagnetic materials in itsconstruction, the fact that the primary moves rather than beingstationary and the advanced signal conditioning electronics controllingits operation, the LVDT of U.S. Pat. No. 7,038,443 provides sensitivityunavailable in previous LVDTs. The FIG. 1 LVDT comprises a movablenon-ferromagnetic coil form 114 around which a primary coil 115 is woundand a stationary non-ferromagnetic coil form or forms 110 around whichtwo secondary coils 103 and 104 are wound. The coil forms can be made ofplastic or paramagnetic material. The primary coil form 114 ismechanically connected to the object of interest (not shown) by a shaft108. The shaft 108 can transmit displacements of the object of intereston the order of microns or smaller. Alternatively the primary coil formcould be stationary and the secondary coil forms could be movable withthe object of interest mechanically connected to the secondary coilforms. The functionality of such a LVDT would be equivalent to thatshown in FIG. 1.

Excitation electronics 111 produce the current driving the primary coil115. As the position of the object of interest attached to shaft 108changes, and therefore the position of the primary coil 115 with respectto the secondary coils 103 and 104 changes, the flux coupled to the twosecondaries, 103 and 104, also changes. These voltages are amplifiedwith a differential amplifier 106 and converted to a voltageproportional to the core displacement by the signal conditioningelectronics 112. For small displacements, the signal is linear. The useof plastic or paramagnetic material in the construction of the FIG. 1LVDT lowers the sensitivity gain that would be provided by highpermeability magnetic material, but eliminates Barkhausen noise. Theelimination of Barkhausen noise permits the output of the excitationelectronics 111 to be raised without causing a corresponding increase inoutput noise, thus increasing the sensitivity of the LVDT.

FIG. 2 shows a more detailed depiction of the digital excitation andsignal conditioning electronics for the FIG. 1 LVDT, taken from USPatent App. Pub. No. US20040056653, Linear Variable DifferentialTransformer with Digital Electronics, by some of the same inventors ashere. The FIG. 2 digital excitation and signal conditioning electronicsare based on a digitally generated square wave, which when filteredproduces a sine wave drive signal with more precisely defined amplitudeand frequency, and lower noise, than a sine wave drive signal generatedby an analog sine wave generator. This digitally generated square waveoriginates in a microprocessor 280. The microprocessor could be adigital signal processor, a microcontroller or other similarmicroprocessors known to those skilled in the art. The square wave inturn is filtered by a low pass filter 224 that effectively removes allthe harmonics of the square wave above the fundamental, resulting in apure sine wave. The filter is optimized to be stable with respect tovariations in temperature. The sine wave in turn is amplified by acurrent buffer 225 that directly drives the LVDT primary 215. A sinewave generated by this excitation circuit has nearly perfect frequencyand amplitude stability and has a high signal to noise ratio.

In the embodiment of the excitation and signal conditioning electronicsdepicted in FIG. 2, one lead from each of the secondaries 103 and 104 isgrounded and the other is connected to a high precision, low noisedifferential amplifier 106 which subtracts the input of one secondaryfrom the input of the other and amplifies the difference mode signal.The differential amplifier is designed to produce low noise when coupledto a low impedance input source (such as a coil). The signal from thedifferential amplifier 106 is input to a buffer amplifier 231 and aninverting buffer amplifier 232. The output of the buffer amplifier 231is fed into a normally closed input of an analog switch 233 while theoutput of the inverting buffer amplifier 232 is fed into a normally openinput of the same switch. This arrangement could be reversed with noloss of functionality as long as the two inputs of the switch are set sothat one input is open when the other input is closed. The action of theanalog switch 233 is controlled by a square wave originating in themicroprocessor 280 which can be phase shifted relative to the squarewave also originating in the microprocessor 280 which (when filtered andamplified) drives the LVDT primary 215. Alternatively to a phase shiftrelative to the primary drive square wave originating in themicroprocessor 280, it is possible to shift the phase relative to thesignal going into the primary drive current buffer 225. All that mattersis that the phase of the primary drive relative to the phase of thereference square wave is adjustable. Preferably, the opening of oneinput which occurs with the closing of the other input of switch 233 is90 degrees out of phase with the output signal from amplifier 106. Theoutput of the analog switch 233 is fed into a stable, low noise, lowpass filter 234. The output of this filter provides a signalproportional to the position of the moving primary coil 215.

Scanning probe devices such as the atomic force microscope (AFM) can beused to obtain an image or other information indicative of the featuresof a wide range of materials with molecular and even atomic levelresolution. As the demand for resolution has increased, requiring themeasurement of decreasingly smaller forces and movements free of noiseartifacts, the old generations of these devices are made obsolete. Thepreferable approach is a new device that addresses the central issue ofmeasuring small forces and movements with minimal noise.

For the sake of convenience, the current description focuses on systemsand techniques that may be realized in a particular embodiment ofscanning probe devices, the atomic force microscope (AFM). Scanningprobe devices include such instruments as AFMs, scanning tunnelingmicroscopes (STMs), 3D molecular force probe instruments,high-resolution profilometers (including mechanical stylusprofilometers), surface modification instruments, NanoIndenters,chemical or biological sensing probes, instruments for electricalmeasurements and micro-actuated devices. The systems and techniquesdescribed herein may be realized in such other scanning probe devices,as well as devices other than scanning probe devices which requireprecision, low noise displacement measurements.

An AFM is a device which obtains topographical information (and/or othersample characteristics) while scanning (e.g., rastering) a sharp tip onthe end of a probe relative to the surface of the sample. Theinformation and characteristics are obtained by detecting changes in thedeflection or oscillation of the probe (e.g., by detecting small changesin amplitude, deflection, phase, frequency, etc.) and using feedback toreturn the system to a reference state. By scanning the tip relative tothe sample, a “map” of the sample topography or other characteristicsmay be obtained.

Changes in the deflection or oscillation of the probe are typicallydetected by an optical lever arrangement whereby a light beam isdirected onto the side of the probe opposite the tip. The beam reflectedfrom the probe illuminates a position sensitive detector (PSD). As thedeflection or oscillation of the probe changes, the position of thereflected spot on the PSD also changes, causing a change in the outputfrom the PSD. Changes in the deflection or oscillation of the probe aretypically made to trigger a change in the vertical position of the baseof the probe relative to the sample (referred to herein as a change inthe Z position, where Z is generally orthogonal to the XY plane definedby the sample), in order to maintain the deflection or oscillation at aconstant pre-set value. It is this feedback that is typically used togenerate an AFM image.

AFMs can be operated in a number of different sample characterizationmodes, including contact modes where the tip of the probe is in constantcontact with the sample surface, and AC modes where the tip makes nocontact or only intermittent contact with the surface.

Actuators are commonly used in AFMs, for example to raster the probeover the sample surface or to change the position of the base of theprobe relative to the sample surface. The purpose of actuators is toprovide relative movement between different parts of the AFM; forexample, between the probe and the sample. For different purposes anddifferent results, it may be useful to actuate the sample or the probeor some combination of both. Sensors are also commonly used in AFMs.They are used to detect movement, position, or other attributes ofvarious components of the AFM, including movement created by actuators.

For the purposes of this specification, unless otherwise indicated (i)the term “actuator” refers to a broad array of devices that convertinput signals into physical motion, including piezo activated flexures;piezo tubes; piezo stacks, blocks, bimorphs and unimorphs; linearmotors; electrostrictive actuators; electrostatic motors; capacitivemotors; voice coil actuators; and magnetostrictive actuators, and (ii)the term “sensor” or “position sensor” refers to a device that convertsa physical quantity such as displacement, velocity or acceleration intoone or more signals such as an electrical signal, and vice versa,including optical deflection detectors (including those referred toabove as a PSD), capacitive sensors, inductive sensors (including eddycurrent sensors), differential transformers (such as described in U.S.Pat. No. 7,038,443 and co-pending applications US Patent App. Pub. No.US20020175677, Linear Variable Differential Transformers for HighPrecision Position Measurements, and US20040056653, Linear VariableDifferential Transformer with Digital Electronics, which are herebyincorporated by reference in their entirety), variable reluctancesensors, optical interferometry, strain gages, piezo sensors andmagnetostrictive and electrostrictive sensors.

SUMMARY OF THE INVENTION

Embodiments describe an LVDT and a method of operating an LVDT.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Prior art showing a LVDT with a low-permeability core and amoving primary.

FIG. 2: Prior art showing excitation and signal conditioning electronicsbased on a synchronous analog switch.

FIG. 3: Preferred embodiment of integrated piezo flexure and LVDT.

FIG. 4: Preferred embodiment of digital excitation and signalconditioning electronics for integrated piezo flexure and LVDT.

FIG. 4A: Preferred embodiment of field programmable gate array fordigital excitation and signal conditioning electronics of FIG. 4.

FIG. 4B: Alternative embodiment of primary drive of digital excitationand signal conditioning electronics of FIG. 4.

FIG. 4C: Alternative embodiment of wiring for secondary of digitalexcitation and signal conditioning electronics of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A piezo activated flexure may be used to move the sample in the X and Ydirections relative to the tip of the probe of an AFM, that is to scanthe sample in the XY plane, using a XY positioning stage like that shownin FIG. 20 of U.S. Pat. No. 7,038,443, by some of the same inventors ashere. Similarly, as shown in FIG. 19 of that patent, such a flexure maybe used to change the vertical position of the base of the proberelative to the sample (that is along the Z axis) using a Z positioningstage in order to maintain the deflection or oscillation of the probetip at a constant pre-set value. In both situations a LVDT like thatdisclosed in U.S. Pat. No. 7,038,443 may be used to sense movement inthe X, Y and Z directions and to make any desired corrections. For thispurpose, what is of interest, the X position and the Y position of theXY positioning stage, and the Z position of the Z positioning stage, iseach mechanically connected to a primary coil form 114 of a separateLVDT via the shaft 108 of the LVDT in question and each primary coilform therefore moves in tandem with any movement of the X position, Yposition or Z position, as the case may be. The secondary coil forms 110of each such LVDT in turn are fastened to the frame of the XYpositioning stage in the case of the LVDTs pertaining to the X positionor the Y position and to the frame of the AFM in the case of the LVDTpertaining to the Z position. The secondary coil forms 110 of each suchLVDT therefore remain stationary relative to its primary coil form 114.

The present invention uses piezo activated flexures to move the samplein the X, Y and Z directions relative to the tip of the probe of an AFM,that is to scan the sample in the XY plane, and to move the verticalposition of the sample relative to the base of the probe, that is tomove the sample or base of the probe in the Z plane, in order tomaintain the deflection or oscillation of the probe tip at a constantpre-set value. These piezo activated flexures are part of a scannermodule of an AFM. An AFM for which these piezo activated flexures may beused is described in a co-pending application, US patent applicationSer. No. 12/587,943, entitled Modular Atomic Force Microscope, by someof the same inventors.

FIG. 3 depicts one of these piezo activated flexures, the one that isused to change the vertical position of the sample relative to the baseof the probe. Piezo activated flexures similar to that depicted in FIG.3 may be used to change to scan the sample in the XY plane. The piezo301 of FIG. 3 is of a stack design known to those versed in the art withtop and bottom indentations to accommodate a top ball bearing 302 and abottom ball bearing 303. The flexure 304 is of a tube design withinterior threads to provide for a threaded disk insert (or contiguousdisk inserts) at the top 305, together with a threaded sample supportplate 307, and another threaded disk insert at the bottom 306. The diskinserts have top and bottom indentations corresponding to those of thepiezo 301 to accommodate the top and bottom ball bearings 302 and 303.The interior threads of the flexure 304 and the threaded disk inserts305 and 306 permit the piezo 301 via the ball bearings 302 and 303 to belocked into place within the flexure 304.

The bottom disk insert 306 of the flexure 304 taken together with thedesign of the flexure itself serve as a cap and permits very littlemotion along the Z axis in the direction of the bottom of the flexure.The top disk insert 305 again taken together with the design of theflexure itself permits free movement of the flexure 304 along the Z axisin the direction of the top of the flexure in accordance with verticalexpansion and contraction of the piezo 301. The cut-outs or recesses 308in the flexure 304 constrain this movement to the Z plane, and permitvery little motion in the X and Y planes.

When the piezo 301 is locked into place within the flexure 304 the topdisk insert 305 is tightened somewhat more than is necessary to lock thepiezo in place as a means of preloading the flexure 304. The cut-outs orrecesses 308 in the flexure 304 transform this additional tighteninginto movement of the flexure, together with the sample support plate 307and thereby the sample (not shown), along the Z axis in the direction ofthe top of the flexure. When the piezo 301 is contracted (using theappropriate electrical charge) the cut-outs or recesses 308 of theflexure 304 transform this contraction into movement of the portion ofthe flexure 304 above the cut-outs or recesses 308, together with thesample support plate 307 and thereby the sample, along the Z axis in thedirection of the bottom of the flexure. When the piezo 301 is expanded(using the appropriate electrical charge) the cut-outs or recesses 308of the flexure 304 transform this expansion into movement of the portionof the flexure 304 above the cut-outs or recesses 308, together with thesample support plate 307 and the sample, along the Z axis in thedirection of the top of the flexure. As noted this motion is accompaniedby very little motion in the X and Y planes.

As already noted, LVDTs like those disclosed in U.S. Pat. No. 7,038,443may be used in an AFM to sense and correct movement in the X, Y or Zdirections when the sample is scanned in the XY plane or when thevertical position of the sample relative to the base of the probe ismoved in the Z plane. As shown in that patent, this is achieved bymechanically connecting the primary and secondaries of LVDTs to theparts of the AFM relevant for the purpose.

The present invention uses LVDTs to sense and correct movement in the X,Y or Z directions in an AFM, but in a very different way than shown inU.S. Pat. No. 7,038,443. Instead of mechanically connecting the primaryand secondary coil forms of LVDTs to the parts of the AFM relevant forthe purpose, here the primary and secondary coil forms are integral tothe parts themselves. As shown in FIG. 3, a channel 309 which serves asthe primary coil form for the LVDT is formed into the top of the flexure304 just above the cut-outs or recesses 308 in the flexure 304. Asdescribed above this portion of the flexure, and therefore the channel309, moves as the piezo 301 is contracted or expanded. Similarly a pairof channels 310 which serve as the secondary coil forms for the LVDT areformed into a stationary sleeve 311 which is fastened to the flexure 304below the cut-outs or recesses 308. As described above the portion ofthe flexure 304 to which the sleeve 311 is attached, and therefore thesleeve, does not move as the piezo 301 is contracted or expanded.

Within the limits imposed by the requirement for preloading the flexure304, loosening or tightening the top disk insert 305 can be used tocenter the channel 309 which serves as the primary coil form for theLVDT relative to the channels 310 which serve as the secondary coilforms.

The flexure 304 provides conduits whereby electrical connections may beestablished with the primary coil, the secondary coils and the piezo301. FIG. 3 shows the exterior portion of one of these conduits 312.

As noted in U.S. Pat. No. 7,038,443 non-ferromagnetic coil forms are animportant contributor to making a sensitive LVDT. For this purpose, thecoil forms could be made of plastic or paramagnetic material. In thepresent invention the flexure 304, in which the channel 309 which servesas the primary coil form is integrated, is preferably fabricated from ahigh-yield-stress non-ferromagnetic aluminum such as 7075 aluminum.Alternatively they could be fabricated from a ceramic material. Thestationary sleeve 311, in which the pair of channels 310 which serve asthe secondary coil forms are integrated, is preferably fabricated from aplastic material such as PEEK. Again, they could also be fabricated froma ceramic material.

FIG. 4 shows a preferred embodiment of digital excitation and signalconditioning electronics for the LVDT of the present invention in whichthe primary and secondary coil forms of the LVDT are integral to therelevant moving parts of a piezo activated flexure like that depicted inFIG. 3 and the coil forms are formed from a non-ferromagnetic material.These electronics may be used with LVDTs of other designs, for examplethe LVDT of FIG. 1 where they would replace the digital excitation andsignal conditioning electronics depicted in FIG. 2.

The embodiment of the digital excitation and signal conditioningelectronics of FIG. 4 are based on a digitally generated sine wave drivesignal with much more precisely defined amplitude and frequency, andlower noise, than a sine wave generated by an analog sine wavegenerator. This sine wave drive signal originates in a direct digitalsynthesizer 401, implemented within the field programmable gate array412, some of the components of which are shown separately in FIG. 4A.The sine wave is then routed though a digital gain stage 402, alsoimplemented within the FPGA 412, which permits the user to control theamplitude of the wave. At this point the sine wave has the followingform:A sin ωt

The sine wave is then converted to analog form by a digital to analogconverter 403 and amplified by a buffer 404 that directly drives theLVDT primary 405 of the present invention typically at a +10V to −10Vvoltage range, but other voltages may be used. The voltages driving theprimary 405 may be doubled through another embodiment depicted in FIG.4B. In that embodiment, the output of the digital to analog converter403 is split and sent both to a gain stage 420 and a negative gain stage421. The output of each stage is in turn connected to one of the leadsof the LVDT primary 405, and the primary is differentially driven attwice the original voltage range.

The signal conditioning electronics of the digital excitation and signalconditioning electronics for the LVDT of the present invention aredepicted in FIG. 4. As shown there, one of the secondaries 408 and 409may be wound in the opposite direction from the winding of the other andthe adjoining leads from the oppositely wound secondaries wiredtogether. The other lead from one of the secondaries, here secondary409, is grounded and the other lead from the second secondary, heresecondary 408, is connected to an analog gain stage 410.

FIG. 4C shows another equivalent arrangement of the secondaries 408 and409 and the analog gain stage 410 of FIG. 4 where the secondary windingsare wound in the same direction, but are wired to produce the sameeffect as with secondaries wound in opposite directions as in FIG. 4.Either arrangement offers a significant improvement in thesignal-to-noise ratio of the signal conditioning electronics for theLVDT of the present invention relative to such electronics of otherLVDTs, for example the electronics depicted in FIG. 2. One reason forthis improvement is the self-cancelling feature of the arrangement. Inthe signal conditioning electronics of the FIG. 2 LVDT, the signalcoupled to one secondary by the primary 215 is subtracted in thedifferential amplifier 106 from the signal coupled to the othersecondary in order to determine a voltage proportional to thedisplacement of the primary coil form 114 and therefore the displacementof the object of interest which is mechanically connected to the coilform. Indeed the differential amplifier 106 is making this calculationeven when the primary is centered exactly between the two secondariesand there is no displacement to measure. With the signal conditioningelectronics for the LVDT of the present invention however the signalcoupled to the secondaries 408 and 409 are wound or wired such thateither the currents induced by the coupled signal in the case of thearrangement shown in FIG. 4 or the voltages so induced in the case ofthe arrangement shown in FIG. 4C oppose each other in the secondariesthemselves, thereby obviating the need for a differential amplifier.This self-opposing phenomenon for example results in a zero signal fromthe secondaries 408 and 409 or 425 and 426, as the case may be, when theprimary 405 is centered exactly between the two secondaries.

The signal-to-noise ratio of the signal conditioning electronics forLVDTs using a differential amplifier 106 like that of the FIG. 2 LVDT isinherently lower than is desirable because of the voltage rails that arepart of such amplifiers. These rails limit the voltages in thesecondaries that can be accommodated by the amplifier to low levels andthus limit the possible signal-to-noise ratio. Furthermore as thevoltage in the secondaries rises, so does Johnson noise, and thereforethe signal-to-noise ratio of the signal conditioning electronicsdeclines.

The self-opposing phenomenon of the signal conditioning electronics forthe LVDT of the present invention makes it possible to use much highervoltages and thus boost the signal-to-noise ratio. One method of doingthis is to increase the voltage (or current) driving the primary 405 andtherefore the voltages (or currents) induced in the secondaries 408 and409 or 425 and 426, as the case may be. As noted above, the embodimentdepicted in FIG. 4B shows a method for doubling the primary voltage (orcurrent) that is used. Another method substantially increases thevoltages (or currents) induced in the secondaries 408 and 409 or 425 and426, as the case may be, by the voltage (or current) of the primary 405by increasing the turns ratio of the secondaries relative to theprimary. As is well known, the voltages (or currents) induced in thesecondaries 408 and 409 or 425 and 426, as the case may be, can beincreased many times over by this method. However, whether the voltages(or currents) induced in the secondaries 408 and 409 or 425 and 426, asthe case may be, are increased by increasing the voltages (or currents)driving the primary 405 or by increasing the turns ratio of thesecondaries relative to the primary, or both, the self-opposingphenomenon of the signal conditioning electronics for the LVDT of thepresent invention passes along to the gain stage 410 only the differencebetween the voltage (or current) induced in one secondary and thatinduced in the other. Thus, a large increase in thesignal-to-noise-ratio may be obtained because the magnitude of the driveor the turns ratio of secondary to primary are no longer limited by theelectronic input range of the differential amplifier imposed by itsvoltage rails.

As shown in FIG. 4, the signal conditioning electronics of the presentinvention routes the output from the secondaries 408 and 409 or 425 and426, as the case may be, through an analog gain stage 410, at whichpoint the output is a 125 kHz sine wave with the following form:B sin(ωt +Φ)

A typical operating frequency might be 125 kHz, although otherfrequencies could be used. This sine wave is then converted into digitalform with an analog to digital converter 411 and sent to the FPGA 412,the components of which are shown separately in FIG. 4A. The digitizedsignal is then fed through a DC blocking filter 430, implemented withinthe FPGA 412, the output of which goes to a digital multiplier circuit431, also implemented within the FPGA 412. The other input to themultiplier circuit 431 is the digital sine wave driving the LVDT primary405 after its phase offset has been adjusted. As indicated above, thissine wave originates in the DDS 401, implemented within the FPGA 412.The phase offset of the digital sine wave driving the LVDT primary isadjusted by the phase offset adjustment circuit 432, also implementedwithin the FPGA 412. The output from the multiplier circuit 431 has thefollowing form:A sin(ωt)×B sin(ωt+Φ)=(A×B)/2(sin(2ωt+Φ)+sin Φ)

In order to increase the resolution provided by the signal conditioningelectronics for the LVDT of the present invention, the ADC 411 used tocovert the sine wave output from the secondaries 408 and 409 or 425 and426, as the case may be, is preferably at least an 18-bit convertersampling at least at a 2 MHz rate. Using such an ADC, this output, whichfor example is a sine wave at 125 kHz after having been passed throughthe analog gain stage 410 which intervenes between the secondaries 408and 409 or 425 and 426, as the case may be, and the ADC 411, is sampledat a rate of 16 samples per cycle, several times the minimum raterequired to capture a sine wave digitally. However the 18-bit resolutionfor each sample provided by the ADC 411 is insufficient to overcomequantization effects and measure displacement at the subnanometerdynamic ranges required for the LVDT of the present invention. Thesolution to this difficulty is found in the fact that the ADC 411 issampling at a 2 MHz rate, a rate much faster than the rate required forcorrecting movement of the piezo flexure of the present invention.Accordingly, some samples are used to create additional resolution ofthe sine wave, a result that may be referred to as bit growth. Theoutput of the ADC 411 sent to the FPGA 412, therefore, is the sine waveoutput from the secondaries 408 and 409 or 425 and 426, as the case maybe, in high resolution digital form.

The output from the multiplier circuit 431 is routed through a low passfilter 433 which filters out the sin (2 ωt+Φ) term, leaving the dc term(A×B)/2 sin Φ. This dc term of the signal is proportional to the changein position of the piezo flexure of the present invention and may beused to correct that position to the position desired.

Although only a few embodiments have been disclosed in detail above,other embodiments are possible and the inventors intend these to beencompassed within this specification. The specification describesspecific examples to accomplish a more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art.

Also, the inventors intend that only those claims which use the words“means for” are intended to be interpreted under 35 USC 112, sixthparagraph. Moreover, no limitations from the specification are intendedto be read into any claims, unless those limitations are expresslyincluded in the claims. The computers described herein may be any kindof computer, either general purpose, or some specific purpose computersuch as a workstation. The computer may be a Pentium class computer,running Windows XP or Linux, or may be a Macintosh computer. Thecomputer may also be a handheld computer, such as a PDA, cellphone, orlaptop.

The programs may be written in C, or Java, Brew or any other programminglanguage. The programs may be resident on a storage medium, e.g.,magnetic or optical, e.g. the computer hard drive, a removable disk ormedia such as a memory stick or SD media, or other removable medium. Theprograms may also be run over a network, for example, with a server orother machine sending signals to the local machine, which allows thelocal machine to carry out the operations described herein.

What is claimed is:
 1. A method, comprising: placing a sample to betested on a top surface of one part of a housing; moving said topsurface with the sample to be tested relative to another part of thehousing, where said one part of said housing is movable relative to theanother part of the housing, and where said moving is in a z-axisdirection substantially perpendicular to said top surface and where saidmoving in the z-axis direction uses a flexure to change a verticalposition of the top surface; and differentially detecting said moving ofsaid top surface with the sample to be tested relative to the anotherpart of the housing and producing an output signal indicative thereof,wherein said top surface includes a screwable connection part whichallows said flexure to be preloaded.
 2. A detector, comprising: ahousing, having a top surface that holds a sample to be tested on onepart of the top surface, and having and side surfaces that areperpendicular to said top surface; said top surface controlled to move,by actuating a moving part to move said top surface with the sample heldon the top surface, said moving part moving one part of the housingrelative to another part of the housing when actuated, where said onepart moves in a z-axis direction substantially perpendicular to said topsurface; and a differential detector, differentially detecting movementof said one part with the sample to be tested on said one part of thehousing relative to the housing and producing an output signalindicative thereof, wherein said one part of said housing includes anenergized primary coil wound on a primary coil surface that issubstantially perpendicular to said top surface, and said another partof said housing includes first and second parts of a secondary coilwound on a secondary coil surface that is substantially perpendicular tosaid top surface.
 3. The detector as in claim 2, wherein said secondarycoil surface includes said side surfaces of said housing.
 4. Thedetector as in claim 2, wherein said sample is moved on said top surfacewith the sample to be tested in x and y directions that aresubstantially perpendicular to each other and parallel to said topsurface, and where a separation is maintained between a probe and saidsample to allow room for movement in said z-axis direction, wherein saidone part of said housing includes an energized primary coil wound on aprimary coil surface that is substantially perpendicular to said topsurface, and said another part of said housing includes first and secondparts of a secondary coil wound on a secondary coil surface that issubstantially perpendicular to said top surface, and separated from saidprimary coil surface in said x and y directions.
 5. The detector as inclaim 4, wherein said secondary coil surface includes said side surfacesof said housing.
 6. The detector as in claim 4, further comprisingelectrically connecting said primary and secondary coils through aconduit in said housing.
 7. The detector as in claim 6, wherein saiddifferential detector has connections to first and second parts of saidsecondary coil.
 8. The detector as in claim 2, further comprisingelectrically connecting said primary and secondary coils through aconduit in said housing.
 9. The detector as in claim 2, wherein saiddifferential detector connects to first and second portions of saidsecondary coil.
 10. The detector as in claim 2, wherein said moving partis a piezo-driven flexure, where said movement is in a z-axis directionsubstantially perpendicular to said top surface and moves said topsurface with the sample to be tested relative to another part of thehousing.
 11. The detector as in claim 2, wherein said housing includes aflexure that has a plurality of surfaces which flex relative to oneanother based on movement of the sample, and which, when flexing, causemovement between said primary coil and said secondary coil, saidmovement being constrained to the z-axis direction with very littlemotion in the direction of x and y axes.
 12. A device as in claim 11,wherein said top surface includes a screwable connection part whichallows said flexure to be preloaded.
 13. A device as in claim 12,wherein said top surface is a spring-loaded surface with the sample tobe tested, where said top surface is moved relative to another part ofthe housing by a piezo-driven flexure, where said movement is in az-axis direction substantially perpendicular to said top surface.
 14. Atransformer device, comprising: a housing, having a first surfaceholding a sample, and said housing having structure allowing said sampleto move relative to said housing along a first axis, and said housinghaving second and third coaxially located surfaces, said second surfaceallowing winding a primary coil thereon, and said third surface allowingwinding of first and second parts of a secondary coil thereon, and saidsecond and third surfaces being movable relative to each other in asubstantially parallel direction to one another along a second axis,where movement along the second axis being a function of the movement ofsaid sample along the first axis based on movement of said sample; andwherein said first surface is a spring-loaded surface, and wherein saidspring loaded surface is moved relative to another part of the housingby a piezo-driven flexure, where said movement is in a z-axis directionsubstantially perpendicular to said spring loaded surface.